Imprecise probability assessment of tipping points in the climate system

Abstract

Major restructuring of the Atlantic meridional overturning circulation, the Greenland and West Antarctic ice sheets, the Amazon rainforest and ENSO, are a source of concern for climate policy. We have elicited subjective probability intervals for the occurrence of such major changes under global warming from 43 scientists. Although the expert estimates highlight large uncertainty, they allocate significant probability to some of the events listed above. We deduce conservative lower bounds for the probability of triggering at least 1 of those events of 0.16 for medium (2-4°C), and 0.56 for high global mean temperature change (above 4°C) relative to year 2000 levels.climate change ͉ expert elicitation

Arctic Climate Tipping Points

“…3). Expert elicitation concurs that above 4°C global warming dieback becomes more likely than not (Supplementary Information of Kriegler et al, 2009). Increasingly warm summers becoming too hot for the currently dominant tree species, increased vulnerability to disease, decreased reproduction rates, and more frequent fires causing significantly higher mortality, all contribute.…”

“…Only Arctic tipping elements for which there is some quantitative information linking a tipping point to global temperature are shown mass balance (Huybrechts and De Wolde 1999). Results from an expert elicitation concur that if global warming exceeds 4°C there is a high probability of passing the tipping point (Kriegler et al 2009). An alternative surface energy balance model predicts a more distant threshold at around 6°C global warming (J. Bamber, personal communication).…”

“…For each tipping point, the transition from white to yellow indicates that its likelihood becomes non-zero, the transition from yellow to red indicates that it becomes as likely as not (best estimate of threshold location), and the appearance of dark red indicates it has become more likely than not. Likelihood information is based on review of the literature, the results of expert elicitation for the GIS, boreal forest and Atlantic THC (Kriegler et al 2009), and interpretation by the present author. Only Arctic tipping elements for which there is some quantitative information linking a tipping point to global temperature are shown mass balance (Huybrechts and De Wolde 1999).…”

“…3). Expert elicitation suggests that THC collapse becomes as likely as not with [4°C warming this century (Kriegler et al 2009). The IPCC (2007) viewed the threshold as even more remote, but recent analysis suggests the models used were systematically biased towards a stable THC .…”

Catastrophic Risk, Precautionary Abatement, and Adaptation Transfers

“…The parameter φ is calibrated such that the probability of a catastrophic occurrence is 16% when the global average temperature increase hits 3°C above the pre-industrial period (φ=0.021). This value has been suggested by a number of recent studies that have elicited the opinion of experts about the likelihood of catastrophic outcomes or of the trespassing of tipping points (Lenton et al, 2008, Kriegler et al, 2009). In the model this occurs at the end of the century.…”